1. Field of the Invention
This invention relates to a magnetic disk cartridge and a process for producing the magnetic disk cartridge. This invention particularly relates to a magnetic disk cartridge, which comprises a cassette shell formed by welding two cassette shell halves to each other, and a process for producing the magnetic disk cartridge.
2. Description of the Prior Art
Magnetic disk cartridges comprise a thin cassette shell and a magnetic disk, which is incorporated in the cassette shell such that it can rotate and on which analog or digital signals are to be recorded magnetically. The cassette shell takes on the form of a flat prismatic shape and comprises an approximately square top surface having an area slightly larger than the area of the magnetic disk, a bottom surface having an opening, through which a center core for supporting the center of the magnetic disk is exposed to the exterior, and a side surface having a narrow width and extending between the periphery of the top surface and the periphery of the bottom surface. The cassette shell is constituted by locating an upper cassette shell half and a lower cassette shell half such that they stand facing each other, and securing them to each other with screws, welding, or the like. The magnetic disk cartridge is provided with openings for insertion of a magnetic head, through which the magnetic head for magnetically recording and reproducing signals is to be inserted from the exterior such that the magnetic head can be brought into contact with the surfaces of the magnetic disk or can be brought to positions close to the surfaces of the magnetic disk. Also, the magnetic disk cartridge is provided with a shutter for opening and closing the openings for insertion of the magnetic head. When the magnetic disk cartridge is not being used, the shutter closes the openings for insertion of the magnetic head such that dust, debris, or the like, may not enter into the magnetic disk cartridge.
Recently, a magnetic disk cartridge, which has a recording capacity that is 50 times as large as the recording capacity of conventional magnetic disk cartridge (3.5-inch FD) by virtue of high-density recording (and is slightly larger than 3.5 inches), has been developed. In the developed magnetic disk cartridge, the magnetic disk is rotated at a markedly higher speed than the speed at which the magnetic disk in the conventional magnetic disk cartridges is rotated. Also, when signals are recorded on the magnetic disk accommodated in the developed magnetic disk cartridge and are reproduced therefrom, the position of the magnetic disk must be adjusted with a very high accuracy with respect to a magnetic head.
In order to satisfy the requirements for the high positioning accuracy, the accuracy of the dimensions of the cassette shell of the magnetic disk cartridge must be high. In particular, the positions of the two cassette shell halves to be combined and secured to each other must be adjusted accurately and must then be secured to each other. For such purposes, welding is advantageous over the use of screws. With welding, there is no risk that looseness or disengagement of the cassette shell halves is produced after they have been secured to each other. However, in order for ultrasonic welding to be carried out, projections or protruding strips (both will hereinbelow be referred to as the projections), which serve as energy directors (ED's) for concentrating energy of ultrasonic waves, must be formed on the surface to be welded. In addition, it is necessary to use a combination of a positioning pin and a pin receiver for accurately adjusting the positions of the two cassette shell halves with respect to each other during the welding. In particular, the projections for the welding are formed on the surfaces of the two cassette shell halves, which face each other. Therefore, if the projections are formed on the surfaces perpendicular to the fitting direction, along which the two cassette shell halves are moved towards each other and brought into contact with each other during the fitting step, the thickness of the entire cassette shell after being formed by the fitting of the two cassette shell halves to each other will fluctuate in accordance with the extent of the welding. Further, shift in positions of the two cassette shell halves and warp thereof occur depending on how the positioning pin and the pin receiver are formed. These problems are detrimental for the cassette shell, which is required to have accurate dimensions.
Also, besides the combination of the positioning pin and the pin receiver described above, it is necessary for protruded structures to be located on the inner surfaces of the cassette shell halves. From the viewpoint of the cost of molds for the molding step, prevention of deformation after the molding step, and product management, it is not desirable to have protruded structures provided on the inner surfaces of the cassette shell halves.
Therefore, it is desired that the structures of the cassette shell halves to be welded to each other by the ultrasonic welding are kept as simple as possible.